Method of preparing polyethylene glycol modified polyester filaments

ABSTRACT

Disclosed is a method of copolymerizing polyethylene glycol (PEG) into polyethylene terephthalate (PET) to achieve a polyethylene glycol-modified polyester composition that can be spun into filaments. The method includes the steps of copolymerizing polyethylene glycol into polyethylene terephthalate in the melt phase to form a copolyester composition, then polymerizing the copolyester composition in the solid phase until the copolyester is capable of achieving a melt viscosity that facilitates the spinning of filaments, and thereafter spinning filaments from the copolyester. A copolyester composition comprised of polyethylene glycol and polyethylene terephthalate is also disclosed. Fabrics made from fibers formed from the copolyester composition possess wetting, wicking, drying, flame-retardancy, static-dissipation, and soft hand properties that are superior to those of fabrics formed from conventional polyethylene terephthalate fibers of the same yarn and fabric construction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of copending U.S. application Ser. No.09/444,192, filed Nov. 19, 1999.

FIELD OF THE INVENTION

The present invention relates to the production of polyethylene glycolmodified polyester fibers. The present invention also relates to themanufacture of yarns and fabrics from these copolyester fibers.

BACKGROUND OF THE INVENTION

Polyester filament is strong, yet lightweight, and has excellent elasticmemory characteristics. Polyester fabric resists wrinkles and creases,retains its shape in garments, resists abrasions, dries quickly, andrequires minimal care. Because it is synthetic, however, polyester isoften considered to have an unacceptable appearance for garment purposeswhen initially formed as a filament. Accordingly, polyester filamentsrequire texturing to produce acceptable characteristics of appearance,hand, and comfort in yarns and fabrics. Even then, polyester is oftenviewed unfavorably in garments.

In pursuit of improved polyesters, various chemical modifications havebeen attempted to obtain desirable textile features. Unfortunately, somesuch treatments can produce unexpected or unwanted characteristics inthe modified polyester. For example, polyethylene glycol enhancescertain polyester properties, such as dye uptake, but diminishes otherproperties, especially those melt phase characteristics that arecritical to filament spinning. Consequently, manufacturers have foundthat significant fractions of polyethylene glycol in copolyester cancomplicate—and even preclude—the commercial production of acceptablecopolyester filaments. To gain commercial acceptance, modifiedpolyesters must be compatible with commercial equipment with respect tomelt-spinning, texturing, yarn spinning, fabric forming (e.g., weavingand knitting), and fabric finishing. This need for processingcompatibility through conventional equipment has constrained thedevelopment of innovative polyester compositions.

To overcome the limitations of polyester compositions, polyester fibersare often blended with other kinds of fibers, both synthetic andnatural. Perhaps most widely used in clothing are blended yarns andfabrics made of polyester and cotton. In general, blended fabrics ofpolyester and cotton are formed by spinning blended yarn from cottonfibers and polyester staple fibers. The blended yarns can then be wovenor knitted into fabrics.

Cotton, like polyester, has certain advantages and disadvantages. Cottonis formed almost entirely of pure cellulose. Cotton fibers are typicallyabout one inch long, but can vary from about one half inch to more thantwo inches. Mature cotton fibers are characterized by theirconvolutions. Under a microscope, cotton appears as a twisted ribbonwith thickened edges. Cotton is lightweight, absorbs moisture quicklyand easily, and has a generally favorable texture (i.e., hand) whenwoven into fabrics. Cotton, however, lacks strength characteristics andelastic memory. Consequently, garments formed entirely of cotton requirefrequent laundering and pressing.

Blends of cotton and polyester fibers have found wide-ranging acceptanceas they combine the desirable characteristics of each. Even so, thereare continuing efforts to develop polyester filament, yarns, and fabricsthat more closely resemble those of cotton, silk, rayon, or othernatural fibers. One example is polyester microfibers, which arecharacterized by extremely fine filaments that offer exceptionally goodaesthetics and hand, while retaining the benefits of polyester.

A need continues to exist, however, for enhanced polyester compositionsthat have properties similar to those of cotton and other naturalfibers, while retaining the advantages of polyester. One suchcomposition and method for producing the same is disclosed by Nicholsand Humelsine in pending U.S. patent application Ser. No. 09/141,665(Polyester Modified with Polyethylene Glycol and Pentaerythritol), whichis commonly assigned with this application. U.S. patent application Ser.No. 09/141,665, which is incorporated entirely herein by reference,discloses a polyester composition that includes polyethyleneterephthalate, polyethylene glycol in an amount sufficient to increasethe wetting and wicking properties of a filament made from thecomposition to a level substantially similar to the properties ofcotton, but less than the amount that would reduce the favorable elasticmemory properties of the polyester composition, and chain branchingagent in an amount that raises the melt viscosity of the polyestercomposition to a level that permits filament manufacture undersubstantially normal spinning conditions. Including significantconcentrations of branching agents to increase melt viscosity, however,is sometimes undesirable because branching agents promote cross-linking.This reduces filament strength, which can lead to processing failures.

OBJECT AND SUMMARY OF THE INVENTION

Therefore, it is an object of this invention to provide polyethyleneglycol modified polyester filaments that possess favorablecharacteristics similar to natural fibers, yet retain the advantages ofpolyester. It is a further object of the present invention to provide amethod of copolymerizing polyethylene glycol (PEG) into polyethyleneterephthalate (PET) to achieve a PEG-modified polyester composition thatis readily spun into filaments, wherein the presence of branching agentsis nonessential.

As is understood by those of ordinary skill in the art, modifyingconventional polyesters with polyethylene glycol can improve certainpolyester characteristics, yet can adversely affect others. For example,adding polyethylene glycol to polyethylene terephthalate improveswetting and wicking, but slows melt-phase polymerization kinetics. Italso depresses melt viscosity and renders the processing of suchPEG-modified polyesters somewhat impractical in commercial polyesterspinning operations.

Accordingly, in one aspect, the invention is a method of copolymerizingpolyethylene glycol into polyethylene terephthalate in a way thatretains the favorable properties of polyethylene glycol while attaininga high intrinsic viscosity. This facilitates the commercial spinning ofthe PEG-modified polyester using conventional spinning equipment. Aswill be understood by those having ordinary skill in the art,copolymerizing polyethylene glycol into polyethylene terephthalate isconventionally achieved by reacting ethylene glycol and eitherterephthalic acid or dimethyl terephthalate in the presence ofpolyethylene glycol.

In brief, polyethylene glycol, which typically makes up between about 4percent and 20 percent by weight of the resulting copolyester, iscopolymerized into polyethylene terephthalate in the melt-phase to arelatively low intrinsic viscosity (i.e., a viscosity that will notsupport filament spinning). The resulting PEG-modified polyester is thenfurther polymerized in the solid phase until the copolyester is capableof achieving a melt viscosity sufficient to spin filaments. Althoughpolyesters having lower intrinsic viscosities can be spun by employinglower temperatures, this is often impractical using conventionalspinning equipment.

By introducing a solid state polymerization (SSP) step, the inventionreduces the need to add branching agents, such as pentaerythritol, toincrease the melt-phase polymerization rate and thereby achieve anintrinsic viscosity that facilitates the spinning of filaments. Althougheffective at increasing polymer viscosity, branching agents promotecross-linking. Cross-linking leads to relatively weaker textiles. Incontrast, the present method achieves a copolyester that contains asignificant proportion of polyethylene glycol without relying onbranching agents to achieve a melt viscosity that is suitable forspinning filaments.

In another aspect, the invention is a method of spinning the modifiedpolyester composition to form partially oriented yarns (POY). Theresulting copolyester POY is particularly suitable for yarns andfabrics, either alone or in a blend with one or more other kinds offibers. In yet another aspect, the invention is a method of spinning themodified polyester composition to form staple filaments, which can bedrawn (and perhaps crimped), and cut into staple fiber. Staple fiber, inturn, can be formed into polyester yarns by employing conventionalspinning techniques. In addition, textured and spun yarns can then beformed into fabrics, preferably by knitting or weaving, either alone orin a blend with one or more other kinds of fibers.

The foregoing, as well as other objectives and advantages of theinvention and the manner in which the same are accomplished, is furtherspecified within the following detailed description and its accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 describes the post-SSP intrinsic viscosity of PEG-modifiedcopolyester versus the weight fraction of polyethylene glycol whenbranching agent is employed in an amount of less than about 0.0014mole-equivalent branches per mole of standardized polymer.

FIG. 2 describes the wicking properties of fabrics formed fromcopolyester filaments produced according to the invention as compared tothe wicking properties of fabrics formed from conventional, unmodifiedpolyethylene terephthalate filaments.

FIG. 3 describes the drying properties of fabrics formed fromcopolyester filaments produced according to the present invention ascompared to the drying properties of fabrics formed from conventional,unmodified polyethylene terephthalate filaments.

FIG. 4 describes the flame-retardancy properties of fabrics formed fromcopolyester filaments produced according to the invention as compared tothe flame-retardancy properties of fabrics formed from conventional,unmodified polyethylene terephthalate filaments.

FIG. 5 describes the static-dissipation properties of fabrics formedfrom copolyester filaments produced according to the invention ascompared to the static-dissipation properties of fabrics formed fromconventional, unmodified polyethylene terephthalate filaments.

FIG. 6 describes the abrasion resistance properties of fabrics formedfrom copolyester filaments produced according to the invention ascompared to the abrasion resistance properties of fabrics formed fromconventional, unmodified polyethylene terephthalate filaments.

FIG. 7 describes the strength properties of fabrics woven fromcopolyester filaments produced according to the present invention ascompared to the strength properties of fabrics woven from conventional,unmodified polyethylene terephthalate filaments.

FIG. 8 describes the improved properties of fabrics formed fromcopolyester filaments produced according to the invention as compared tothe properties of fabrics formed from conventional, unmodifiedpolyethylene terephthalate filaments.

DETAILED DESCRIPTION

In its broadest aspect, the present invention is a method of preparingPEG-modified copolyester filaments by copolymerizing polyethylene glycolinto polyethylene terephthalate in the melt phase to form a copolyestercomposition, then polymerizing the copolyester composition in the solidphase until the copolyester is capable of achieving a melt viscositythat facilitates the spinning of filaments, and thereafter spinningfilaments from the copolyester.

In another aspect, the method of preparing PEG-modified copolyesterfilaments includes copolymerizing polyethylene glycol and chainbranching agent into polyethylene terephthalate in the melt phase toform a copolyester composition. The polyethylene terephthalate ispresent in the copolyester composition in an amount sufficient for afilament made from the copolyester composition to possess dimensionalstability properties substantially similar to those of conventionalpolyethylene terephthalate filaments. The polyethylene glycol, which hasan average molecular weight less than about 5000 g/mol, is present in anamount sufficient for a filament made from the copolyester compositionto possess wicking, drying, and static-dissipation properties that aresuperior to those of conventional polyethylene terephthalate filaments.If used, the total amount of chain branching agent is present in thecopolyester composition in an amount of less than about 0.0014mole-equivalent branches per mole of standardized polymer. (As discussedherein, to describe the molar fraction of branching agent consistently,mole-equivalent branches are referenced to unmodified polyethyleneterephthalate.) The resulting copolyester composition is furtherpolymerized in the solid phase until the copolyester is capable ofachieving a melt viscosity that facilitates the spinning of filaments.Finally, filaments are spun from the copolyester.

The terms “melt viscosity” and “intrinsic viscosity” are used herein intheir conventional sense. Melt viscosity represents the resistance ofmolten polymer to shear deformation or flow as measured at specifiedconditions. Melt viscosity is primarily a factor of intrinsic viscosity,shear, and temperature. As used herein, the term “melt viscosity” refersto “zero-shear melt viscosity” unless indicated otherwise.

Intrinsic viscosity is the ratio of the specific viscosity of a polymersolution of known concentration to the concentration of solute,extrapolated to zero concentration. Intrinsic viscosity is directlyproportional to average polymer molecular weight. See, e.g., Dictionaryof Fiber and Textile Technology, Hoechst Celanese Corporation (1990);Tortora & Merkel, Fairchild's Dictionary of Textiles (7^(th) Edition1996). As used herein, average molecular weight refers to number-averagemolecular weight, rather than weight-average molecular weight.

Both melt viscosity and intrinsic viscosity, which are widely recognizedas standard measurements of polymer characteristics, can be measured anddetermined without undue experimentation by those of ordinary skill inthis art. For the intrinsic viscosity values described herein, theintrinsic viscosity is determined by dissolving the copolyester inorthochlorophenol (OCP), measuring the relative viscosity of thesolution using a Schott Autoviscometer (AVS Schott and AVS 500Viscosystem), and then calculating the intrinsic viscosity based on therelative viscosity. See, e.g., Dictionary of Fiber and TextileTechnology (“intrinsic viscosity”).

In particular, a 0.6-gram sample (+/−0.005 g) of dried polymer sample isdissolved in about 50 ml (61.0-63.5 grams) of orthochlorophenol at atemperature of about 105° C. Fiber and yarn samples are typically cutinto small pieces, whereas chip samples are ground. After cooling toroom temperature, the solution is placed in the viscometer and therelative viscosity is measured. As noted, intrinsic viscosity iscalculated from relative viscosity.

In accordance with the invention, copolyester characteristics can betailored for specific applications by altering the polyethylene glycolcontent. This permits choice in designing fabrics made with copolyesteror copolyester blends according to the present invention. In this sense,the invention establishes a technology family. For example, the weightfraction and the molecular weight of the polyethylene glycol can beadjusted to produce specific effects, such as wetting, drying, dyerates, and softness. Similarly, such modifications can improve the dyestrike rate and reduce the dye usage. In particular, higher polyethyleneglycol fractions, (e.g., greater than about 4 weight percent), result insofter fabrics that wick faster, dry quicker, and dye darker.

In preferred embodiments, the polyethylene glycol is present in thecopolyester composition in an amount between about 4 weight percent and20 weight percent. When amounts of polyethylene glycol greater thanabout 20 weight percent are present, the resulting copolyester does notpolymerize efficiently. Moreover, at such elevated polyethylene glycolfractions, the copolyester composition is difficult to store andtransport for it tends to crystallize, causing undesirable sticking andclumping. Consequently, polyethylene glycol amounts between about 8weight percent and 14 weight percent are more preferred, and amountsbetween about 10 weight percent and 12 weight percent are mostpreferred. Furthermore, while polyethylene glycol with molecular weightsbetween about 200 and 5000 g/mol may be effectively employed, thepreferred average molecular weight for polyethylene glycol is betweenabout 300 and 1000 g/mol, most preferably 400 g/mol.

As known to those familiar with the manufacture of polyester, theequipment used to spin polyester into filaments is designed, built, andadjusted to process polymers whose melt viscosity falls within a certainrange, typically between about 1500 and 4000 poise. Thus, such equipmentruns most satisfactorily when the melt viscosity of the copolyester,which is directly proportional to the intrinsic viscosity as discussedherein, is within this viscosity range. If polyethylene glycol isincluded in relatively significant amounts (i.e., more than about 4weight percent), a number of spinning failures are likely to occur whenconventional polymerization methods are followed. In other words, highpolyethylene glycol fractions can suppress melt viscosity, which in turncan hinder spinning productivity.

The present invention provides a method for incorporating into polyesterthe favorable properties of polyethylene glycol, particularly itsoutstanding wetting and wicking properties. The invention accomplishesthis by employing a higher intrinsic viscosity to compensate for thetendency of higher fractions of polyethylene glycol to lower the meltviscosity of the copolyester. Consequently, the present method virtuallyeliminates the need for significant amounts of branching agent. As willbe understood by those of skill in the art, a low melt viscosity hindersthe processing of copolyester through conventional spinning equipment.

Initially, polyethylene glycol is polymerized into polyethyleneterephthalate in the melt phase to form a copolyester composition.Except for its premature termination, the melt polymerization otherwisefollows conventional techniques that are well known in the art. Thismelt polymerization of the copolyester composition, however, is followedby a solid state polymerization step. Conventional wisdom has held thatan SSP step is unnecessary and even undesirable with respect to formingcopolyester filaments.

In particular, the copolyester composition is polymerized in the solidphase until the copolyester is capable of achieving a zero-shear meltviscosity of at least about 2000 poise at 260° C. It will be understoodby those having ordinary skill in the art that, as used herein, thedescription of polymerizing the copolyester composition in the solidphase until the copolyester is capable of achieving a certain meltviscosity simply means that the solid copolyester would have thatparticular melt viscosity if it were melted without further solid statepolymerization.

In a preferred embodiment of the method, when the weight fraction ofpolyethylene glycol in the copolyester composition is between about 10percent and 12 percent, the copolyester composition is polymerized inthe solid phase until the copolyester is capable of achieving a meltviscosity of between about 2500 and 3000 poise at a temperature of 260°C. As will be understood by those having ordinary skill in this art, thecopolyester need not be spun immediately after undergoing solid statepolymerization. In fact, in preferred embodiments, the copolyester isformed into chips after the step of copolymerizing polyethylene glycolinto polyethylene terephthalate in the melt phase and before the step ofpolymerizing the copolyester composition in the solid phase.

According to the present method, copolyester filaments are preferablyspun at a temperature between about 260° C. and 300° C. This temperaturerange comports with that employed in conventional spinning equipmentthat uses Dowtherm A vapor heat transfer media, which is available fromDow Chemical Co.

As discussed previously, in its broadest aspects, the method includesforming polyethylene glycol modified copolyester filaments bycopolymerizing polyethylene glycol into polyethylene terephthalate inthe melt phase to form a copolyester composition, then polymerizing thecopolyester composition in the solid phase until the copolyestercomposition is capable of achieving a melt viscosity that facilitatesthe spinning of filaments, and thereafter spinning filaments from thecopolyester. FIG. 1 defines the preferred intrinsic viscosity of thecopolyester after solid state polymerization as a function of the weightfraction of polyethylene glycol when low levels of branching agent areemployed (e.g., less than 500 ppm of pentaerythritol).

In preferred embodiments, polyethylene glycol is copolymerized intopolyethylene terephthalate in the melt phase to an intrinsic viscosityof less than about 0.65 dl/g. In one preferred embodiment, the meltphase copolymerization is terminated before the copolyester compositionreaches an intrinsic viscosity of about 0.60 dl/g. In another preferredembodiment, the melt phase copolymerization is terminated before thecopolyester composition reaches an intrinsic viscosity of about 0.55dl/g.

As will be understood by those having ordinary skill in the art,modified polyethylene terephthalate having an intrinsic viscosity ofless than 0.65 dl/g, more than about 4 weight percent polyethyleneglycol, and low levels of branching agent is not readily spun intofilaments. Consequently, after the melt polymerization step, thePEG-modified copolyester composition is polymerized in the solid phaseto an intrinsic viscosity greater than the intrinsic viscosity achievedvia the melt polymerization. For example, when the weight fraction ofpolyethylene glycol in the copolyester composition is about 5 percent,the copolyester composition is preferably polymerized in the solid phaseto an intrinsic viscosity of between about 0.67 and 0.78 dl/g.Similarly, when the weight fraction of polyethylene glycol in thecopolyester composition is about 10 percent, the copolyester compositionis preferably polymerized in the solid phase to an intrinsic viscosityof between about 0.73 and 0.85 dl/g. Finally, when the weight fractionof polyethylene glycol in the copolyester composition is about 15percent, the copolyester composition is preferably polymerized in thesolid phase to an intrinsic viscosity of between about 0.80 and 0.93dl/g. More generally, the target intrinsic viscosity for anypolyethylene glycol weight fraction between about 5 percent and 15percent is defined by the shaded region in FIG. 1.

It will be understood to those of skill in the art that the polyethyleneglycol reduces melt temperature (T_(m)) and glass transition temperature(T_(g)). Consequently, the temperature at which dyes will penetrate themodified polyester structure is lowered. Accordingly, the present methodfurther comprises dyeing the copolyester filaments at a temperature ofless than about 240° F. In one preferred embodiment, the method includesdyeing the copolyester filaments at a temperature of less than about230° F. In yet another preferred embodiment, the method includes dyeingthe copolyester filaments at a temperature of less than about 220° F. Infact, the copolyester filaments can be dyed at or below the temperaturedefined by the boiling point of water at atmospheric pressure (i.e.,212° F. or 100° C.). In fact, the copolyester fibers have achievedexcellent color depth when dyed at 200° F.

As used herein, the concept of dyeing copolyester filaments includesdyeing not only filaments (e.g., partially oriented yarn filaments), butalso staple fibers cut from filaments. Moreover, this concept furtherincludes dyeing copolyester fibers that are formed into yarns orfabrics, either alone or in blends with one or more other kinds of fiber(e.g., cotton or spandex fibers).

In one particular embodiment, the method of preparing PEG-modifiedcopolyester filaments includes reacting in the melt phase ethyleneglycol and either terephthalic acid and dimethyl terephthalate in thepresence of polyethylene glycol to form a copolyester composition havingan intrinsic viscosity of less than about 0.65 dl/g. Preferably, theweight fraction of polyethylene glycol in the resulting copolyestercomposition is between about 4 percent and 20 percent. The copolyestercomposition is thereafter polymerized in the solid phase until thecopolyester is capable of achieving a melt viscosity of at least about2000 poise when heated to 260° C. Finally, filaments are spun from thecopolyester. Additionally, the resulting copolyester filaments may bedyed at a temperature of less than about 240° F.

As noted, in one aspect the method of preparing PEG-modified copolyesterfilaments includes copolymerizing polyethylene glycol and chainbranching agent into polyethylene terephthalate in the melt phase toform a copolyester composition. The polyethylene terephthalate ispresent in an amount sufficient for a filament made from the copolyestercomposition to possess dimensional stability properties (e.g., shrinkageduring home laundering) substantially similar to those of conventionalpolyethylene terephthalate filaments. The polyethylene glycol, which hasan average molecular weight less than about 5000 g/mol, is present in anamount sufficient for filaments made from the copolyester composition topossess wetting, wicking, drying, flame retardancy, andstatic-dissipation properties that are superior to those of conventionalpolyethylene terephthalate filaments. It has been further observed thatfabrics formed according to the present invention possess significantlyimproved hand (i.e., tactile qualities) as compared to conventionalpolyester fabrics made of fibers having similar denier per filament(DPF).

As discussed previously, at least about 4 weight percent polyethyleneglycol is necessary to achieve these improved filament characteristics.When used, chain branching agent is present in the copolyestercomposition in an amount of less than about 0.0014 mole-equivalentbranches per mole of standardized polymer. The resulting copolyestercomposition is further polymerized in the solid phase until thecopolyester is capable of achieving a melt viscosity that facilitatesthe spinning of filaments. Finally, filaments are spun from thecopolyester.

FIG. 2 describes the wicking properties of fabrics formed fromcopolyester filaments produced according to the invention as compared tothe wicking properties of fabrics formed from conventional, unmodifiedpolyethylene terephthalate filaments. Wicking properties were measuredusing 1″×7″ strips that were suspended vertically above water-filledbeakers and then submersed one inch below the water surface. After oneminute, the water migration up the test strips was measured. The fabricswere tested in both fabric directions and averaged. The test stripfabrics were laundered once before testing. The room conditions wereASTM standard 21° C. and 65 percent relative humidity.

FIG. 3 describes the drying properties of fabrics formed fromcopolyester filaments produced according to the present invention ascompared to the drying properties of fabrics formed from conventional,unmodified polyethylene terephthalate filaments. Drying rate wasdetermined using a Sartorius MA30-000V3 at 40° C. Two or three drops ofwater were placed on the fabrics. Then, the evaporation time wasmeasured and an evaporation rate was calculated. The room conditionswere ASTM standard 21° C. and 65 percent relative humidity.

FIG. 4 describes the flame-retardancy properties of fabrics formed fromcopolyester filaments produced according to the invention as compared tothe flame-retardancy properties of fabrics formed from conventional,unmodified polyethylene terephthalate filaments. The testing wasperformed in accordance with the NFPA 701 Method small-scale-after-flametest. FIG. 4 merely shows that fabrics formed from copolyester filamentsproduced according to the invention have better flame-retardancyproperties as compared to those of fabrics formed from conventional,unmodified polyethylene terephthalate filaments. FIG. 4 is not intendedto imply that fabrics formed from copolyester filaments producedaccording to the invention will meet any particular governmentflammability standards.

FIG. 5 describes the static-dissipation properties of fabrics formedfrom copolyester filaments produced according to the invention ascompared to the static-dissipation properties of fabrics formed fromconventional, unmodified polyethylene terephthalate filaments. Staticdissipation was determined using a Rothschild Static-Voltmeter R-4021.In brief, fabric was mounted between the electrodes, and then the timefor the voltage across the fabric to reduce from 150 volts to 75 voltswas measured. The room conditions were ASTM standard 21° C. and 65percent relative humidity. As will be understood by those havingordinary skill in the art, a shorter charge half-life is desirable infabrics because it means fabric static is dissipated faster.

FIG. 6 describes the abrasion resistance properties of fabrics formedfrom copolyester filaments produced according to the invention ascompared to the abrasion resistance properties of fabrics formed fromconventional, unmodified polyethylene terephthalate filaments. Thefabrics each had a TiO₂ level of 3000 ppm. Abrasion resistance wasdetermined using Stoll flat (knits) ASTM D 3886 method and Taber(wovens) ASTM D 3884 method.

FIG. 7 describes the strength properties of fabrics woven fromcopolyester filaments produced according to the present invention ascompared to the strength properties of fabrics woven from conventional,unmodified polyethylene terephthalate filaments. The somewhat weakerstrength of fabrics formed from the filaments prepared according to theinvention reduces undesirable pilling. Fabric strength was determined bystrip test (wovens) ASTM D 1682-64 method or by Ball Burst (knits) ASTMD3787-80A.

FIG. 8 summarizes on a percentage basis the improved properties offabrics formed from copolyester filaments produced according to theinvention as compared to the properties of fabrics formed fromconventional, unmodified polyethylene terephthalate filaments.

Preparing PEG-modified copolyester filaments according to the inventionnot only yields certain improved textile characteristics, but alsoretains the desirable dimensional stability of ordinary polyester.Despite the significant concentration of polyethylene glycol,copolyester filaments prepared according to the invention havedimensional stability properties, especially shrinkage during homelaundering, that are substantially similar to those of conventionalpolyethylene terephthalate filaments. For example, conventionalpolyester fabric exhibits less than about five percent shrinkage in homelaundering if finished at a fabric temperature at or above 350° F.Similarly, copolyester fabric of the invention exhibits less than aboutfive percent shrinkage in home laundering if finished at a fabrictemperature at or above only 330° F.

It is also expected that fabrics formed from the filaments spunaccording to the invention will possess better elastic-memory properties(i.e., stretch and recovery) as compared to fabrics formed fromconventional polyethylene terephthalate filaments.

The commonly-assigned patent application Ser. No. 09/141,665 disclosesthat chain branching agents can raise the melt viscosity of PEG-modifiedcopolymer melt to within the range of normal, unmodified polyethyleneterephthalate. In contrast, the present invention introduces analternative method of producing filament from PEG-modified copolyesterwithout resorting to significant fractions of branching agent.

In accordance with this aspect of the invention, the total amount ofchain branching agent in the copolyester is insufficient to raise themelt viscosity of the copolyester composition to a level that wouldpermit the manufacture of copolyester filament under conditions (e.g.,spinning temperature) that are substantially the same as those underwhich filament can be formed from unmodified polyethylene terephthalate.More specifically, chain branching agent is present in the copolyestercomposition in an amount of less than about 0.0014 mole-equivalentbranches per mole of standardized polymer.

As used herein, the term “mole-equivalent branches” refers to thereactive sites available for chain branching on a molar basis (i.e., thenumber of reactive sites in excess of the two required to form a linearmolecule). For example, pentaerythritol is a tetrafunctional branchingagent, so it possesses two available chain branching reactive sites.

In addition, as used herein, the term “standardized polymer” refers tothe repeat unit of unmodified polyethylene terephthalate, which has amolecular weight of 192 g/mol. In this regard, it will be understood bythose of skill in the art that, for a given total weight of polyethyleneterephthalate, polyethylene glycol, and branching agent, increasing therelative weight fraction of polyethylene glycol, which preferably has amolecular weight of between about 200 g/mol and 5000 g/mol, willdecrease total moles. (This is so because the molecular weight ofpolyethylene terephthalate is less than the molecular weight of thepolyethylene glycol.) Consequently, to maintain uniformity acrossvarious concentrations and molecular weights of polyethylene glycol, thechain branching agent concentration of preferably less than about 0.0014mole-equivalent branches per mole of standardized polymer is based onthe repeat unit of unmodified polyethylene terephthalate. In otherwords, the weight fraction of branching agent should be calculated as ifthe polymer is made of only unmodified polyethylene terephthalate.Consequently, the weight fraction of polyethylene glycol (e.g.,preferably between about 4 weight percent and 20 weight percent) and themolecular weight of the polyethylene glycol (e.g., preferably betweenabout 200 g/mol and 5000 g/mol) can be disregarded in calculatingmole-equivalent branches per mole of standardized polymer.

For example, an amount of pentaerythritol less than about 0.0014mole-equivalent branches per mole of the copolyester composition isequivalent to a weight fraction of less than about 500 ppm when based onthe standardized polymer of unmodified polyethylene terephthalate, whoserepeat unit has a molecular weight of about 192 g/mol. To furtherillustrate this relationship, assume 1000 grams of startingmaterials—500 ppm pentaerythritol, which has a molecular weight of136.15 g/mol, and the remainder polyethylene terephthalate. This isequivalent to 0.5 gram pentaerythritol, or 0.00367 moles ofpentaerythritol, and 999.5 grams polyethylene terephthalate, or 5.21moles polyethylene terephthalate repeat units. The mole fraction ofpentaerythritol relative to the polyethylene terephthalate is,therefore, 0.0705 mole percent (i.e., 0.00367 moles of pentaerythritol÷5.21 moles polyethylene terephthalate). As noted, pentaerythritol hastwo available chain branching reactive sites. Thus, the mole-equivalentbranches per mole of unmodified polyethylene terepthalate is 0.14percent (i.e., 0.0014 mole-equivalent branches per mole of standardizedpolymer).

The weight fraction corresponding to 0.0014 mole-equivalent branches permole of standardized polymer can be estimated for any branching agentusing the following equation:

branching agent (ppm)=(MEB÷CBRS)·(BAMW÷SPMW)·10⁶,

wherein

MEB=0.0014 mole-equivalent branches per mole of standardized polymer

CBRS=number of available chain branching reactive sites

BAMW=molecular weight of the branching agent (g/mol)

SPMW=192 g/mol—molecular weight of the standardized polymer (i.e.,unmodified polyethylene terephthalate)

It will be appreciated by those of skill in the chemical arts that ifthe mole-equivalent branches were not referenced to a mole ofstandardized polymer, a branching agent concentration of 0.0014mole-equivalent branches per mole of polymer (i.e., the copolyestercomposition) would translate to a slightly lower weight fraction, (i.e.,ppm), when a greater polyethylene glycol weight fraction is used, orwhen polyethylene glycol having a higher average molecular weight isemployed. For example, if mole-equivalent branches per mole of polymerwere not related to a common standard, but rather to the actualcomponents of the copolyester composition, an amount of pentaerythritolless than about 0.0014 mole-equivalent branches per mole of thecopolyester composition would be equivalent to a weight fraction of lessthan about 450 ppm when based on polyethylene terephthalate that ismodified by 20 weight percent polyethylene glycol having an averagemolecular weight of about 400 g/mol. Likewise, an amount ofpentaerythritol less than about 0.0014 mole-equivalent branches per moleof the copolyester composition would be equivalent to a weight fractionof less than about 400 ppm when based on polyethylene terephthalate thatis modified by 20 weight percent polyethylene glycol having an averagemolecular weight of about 5000 g/mol. By employing unmodifiedpolyethylene terephthalate as the standardized polymer, however, anamount of pentaerythritol less than about 0.0014 mole-equivalentbranches per mole of standardized polymer is equivalent to a weightfraction of less than about 500 ppm regardless of the weight fraction ormolecular weight of the polyethylene glycol.

To the extent a chain branching agent is employed, the chain branchingagent is preferably a trifunctional or tetrafunctional alcohol or acidthat will copolymerize with polyethylene terephthalate. As will beunderstood by those skilled in the art, a trifunctional branching agenthas one reactive site available for branching and a tetrafunctionalbranching agent has two reactive sites available for branching.Acceptable chain branching agents include, but are not limited to,trimesic acid (C₆H3 (COOH)₃), pyromellitic acid (C₆H₂(COOH)4),pyromellitic dianhydride, trimellitic acid, trimellitic anhydride,trimethylol propane (C₂H₅C(CH₂OH)₃), and preferably pentaerythritol(C(CH₂OH)₄), If the total number of reactive sites exceeds four perbranching agent molecule, steric hindrance may prevent fullpolymerization at the available reactive sites such that more branchingagent may be required to achieve the desired mole-equivalent branches.See, e.g., U.S. Pat. Nos. 4,092,299 and 4,113,704 by MacLean and Estes.

Accordingly, in one particular embodiment, the method of preparingPEG-modified copolyester filaments includes copolymerizing polyethyleneglycol and chain branching agent into polyethylene terephthalate in themelt phase to form a copolyester composition having an intrinsicviscosity of less than about 0.65 dl/g. As will be understood by thosehaving ordinary skill in the art, copolymerizing polyethylene glycol andbranching agent into polyethylene terephthalate is conventionallyachieved by reacting ethylene glycol and either terephthalic acid ordimethyl terephthalate in the presence of polyethylene glycol andbranching agent.

The polyethylene terephthalate is present in an amount sufficient for afilament made from the copolyester composition to possess elastic memoryand dimensional stability properties substantially similar to those ofconventional polyethylene terephthalate filaments. The polyethyleneglycol, which has an average molecular weight less than about 5000g/mol, is present in an amount sufficient for a filament made from thecopolyester composition to possess wicking, drying, andstatic-dissipation properties that are superior to those of conventionalpolyethylene terephthalate filaments. Moreover, the total amount ofchain branching agent that is present in the copolyester composition isless than about 0.0014 mole-equivalent branches per mole of standardizedpolymer.

After the melt polymerization step, the copolyester composition is solidstate polymerized until the copolyester is capable of achieving a meltviscosity of at least about 2000 poise when heated to 260° C. Finally,filaments are spun from the copolyester composition. In addition, theresulting copolyester filaments may be dyed at a temperature of lessthan about 240° F.

In brief, the solid phase polymerization step following the meltpolymerization step produces a melt viscosity for the PEG-modifiedpolyester sufficient for practical processing, and sufficient spinningtensions for a stable and high-throughput commercial process. This is sodespite the presence of only insignificant amounts of branching agent(i.e., less than about 0.14 percent mole-equivalent branches per mole ofstandardized polymer).

A distinct advantage of the present method is that it produces acopolyester filament that, while possessing wetting, wicking, drying,soft hand, flame-retardancy, abrasion-resistance, and static-dissipationproperties that are superior to those of conventional polyethyleneterephthalate filaments, can be processed using conventional textileequipment. For example, in one broad aspect, the PET-modifiedcopolyester can be spun into partially oriented yarns (POY). As will beunderstood by those having ordinary skill in the art, POY is oftencomprised of from tens to hundreds of intermingled filaments (e.g.,between 30 and 200) that are extruded from a spinneret at speedstypically between about 2000 and 4000 meters per minute. The POY is thentypically drawn to form a drawn yarn, (e.g., by draw texturing, flatdrawing, or warp drawing). Thereafter, the drawn yarn is formed intofabric, which is typically finished as well. As will be known by thoseskilled in the art, texturing can be effected in numerous ways, such asair jet, gear crimping, and false-twist techniques.

It should be noted that flat drawn POY produced according to theinvention results in yarns having dyeing characteristics similar tothose of cellulose acetate yarns. These copolyester yarns are especiallysuitable for producing suit linings. As will be known to those havingordinary skill in the art, suit linings are conventionally jig dyedusing low-energy dyes, which have poor fastness properties. The yarnsand fabric formed according to the invention, however, can be dyed onconventional jig dyeing equipment using high-energy dyes, which havebetter fastness.

Because of the characteristic advantages that the invention brings tothe polyester compositions described herein, the resulting polyesterfilaments are particularly useful in blended yarns and blended fabrics.Accordingly, copolyester POY can be blended with at least one other kindof fiber (i.e., a fiber having a different chemical composition orhaving been differently processed) to form a blended yarn. As will beunderstood by those familiar with textile processes, the copolyester POYis typically either draw textured to form a draw textured yarn (DTY) orflat drawn to form a flat-drawn yarn (i.e., a hard yarn) beforeblending. The drawn copolyester yarn is especially suitable for blendingwith cotton fibers, rayon fibers, polypropylene fibers, acetate fibers,nylon fibers, spandex fibers, and conventional polyester fibers.

Furthermore, the drawn copolyester yarn (e.g., DTY or hard yarn) canalso be blended with a least one other kind of fiber to form blendedfabric. In this regard, the drawn copolyester yarn is especiallysuitable for blending with cotton fibers, rayon fibers, polypropylenefibers, acetate fibers, nylon fibers, spandex fibers, conventionalpolyester fibers, and even copolyester staple fibers of the presentinvention. It will be understood that, as used herein, the concept offorming a blended fabric from the drawn copolyester yarn and at leastone other kind of fiber not only includes directly forming a fabric fromthe drawn copolyester yarn and a second kind of fiber, but also includesfirst forming a blended yarn before forming the blended fabric. Ineither case, however, the blended fabric is formed from a drawncopolyester yarn and a second kind of fiber.

As will be known to those skilled in the art, two different kinds offilaments are not usually textured together unless they can use the sametemperature and draw ratio. Consequently, it is desirable to form ablended fabric without first forming a blended yarn when the second kindof fiber has different texturing requirements than those of thecopolyester POY.

It has been observed, however, that the copolyester POY and nylon yarnrequire similar texturing temperatures. Accordingly, in a preferredembodiment, the copolyester POY and a nylon yarn are formed into ablended yarn. Thereafter, the blended yarn is textured. Interestingly,because of dye selectivity, the resulting blended yarn may be dyed withdisperse dye, which preferentially dyes the copolyester component, andacid-based dye, which preferentially dyes the nylon component. In thisway, a heather yarn (or a two-colored yarn) can be produced, which maythen be formed into an attractive, heather fabric (or a two-coloredfabric).

In another broad aspect, the invention further includes cutting thecopolyester filaments into staple fibers. As will be understood by thosehaving ordinary skill in the art, perhaps thousands of filaments can bespun from a single spinneret, typically at speeds of between about 500and 2000 meters per minute. The filaments, often from numerous spinneretpositions, are combined into a tow. The tow is often crimped before thefilaments are cut into staple fibers.

The staple fibers can be formed into yarn using any conventionalspinning technique, such as ring spinning, open-end spinning, and airjet spinning. In this regard, open end and air jet spinning are becomingincreasingly more preferred for polyester yarns, as well as for blendedyarns containing polyester. The yarns formed from the copolyesterfilaments of the invention, in turn, can be woven or knitted intofabrics that have the advantageous characteristics referred to herein.Alternatively, the staple fibers can be formed directly into a non-wovenfabric. As used herein, the concept of forming staple fibers into fabricincludes first forming a yarn, (e.g., knitting and weaving), in additionto forming the staple fibers directly into fabric, (e.g., non-wovenfabric).

In another aspect, the method includes blending the staple copolyesterfibers with at least a second kind of fiber, such as cotton fibers,rayon fibers, polypropylene fibers, acetate fibers, nylon fibers,spandex fibers, and conventional unmodified polyester fibers. In thisregard, acetate fibers and spandex fibers are usually in filament form.Thereafter, the staple fibers and the second kind of fiber can be spuninto yarn, and the yarn formed into fabric using conventionaltechniques. Alternatively, the staple fibers and the second kind offiber can be formed directly into a non-woven fabric.

In yet another aspect, the invention includes forming copolyester fibersfrom the copolyester composition, and then blending the copolyesterfibers with spandex fibers. As used herein, the term “copolyester fiber”broadly refers to uncut filament (e.g., POY) and cut fiber (e.g., staplefiber).

For example, the copolyester fibers and the spandex fibers can beblended into yarn. In one preferred embodiment, this comprises corespinning copolyester staple fibers around a core of spandex filaments.Likewise, in another preferred embodiment, the copolyesterfilaments—preferably in the form of POY—are wrapped around spandexfilaments.

The copolyester fibers and the spandex fibers may also be formed intofabric using conventional techniques. For example, the fabric may beformed, (e.g., woven or knitted), from a blended yarn that is spun fromthe copolyester fibers and the spandex fibers. Alternatively, thecopolyester fibers and spandex fibers may be directly formed into afabric, preferably a knit fabric. To accomplish this, the spandex islaid into a copolyester knit by employing an appropriate knittingmachine attachment.

As noted previously, the invention can include dyeing the copolyesterfibers at a temperature of less than about 240° F. In particular, thisreduction in dyeing temperature not only reduces energy usage, but alsopermits copolyester fibers that are produced according to thisembodiment of the invention to be more effectively combined with spandexfilaments. Blended yarns and fabrics that are made from PEG-modifiedcopolyester fibers—preferably staple fibers or POY—and spandex fiberscan be dyed at temperatures of less than about 240° F., and yet canachieve excellent fastness and depth of color. In one preferredembodiment, the spandex fibers and the copolyester fibers may be dyed ata temperature of less than about 230° F. In another preferredembodiment, the spandex fibers and the copolyester fibers may be dyed ata temperature of less than about 220° F. In yet another preferredembodiment, the spandex fibers and the copolyester fibers may be dyed ator below a temperature of less than the boiling point of water atatmospheric pressure (i.e., 212° F. or 100° C.). In this regard, itshould be understood that the concept of dyeing copolyester fibers andspandex fibers includes dyeing the blend in the form of blended yarnsand blended fabrics. It is emphasized that, as used herein, the term“copolyester fibers” broadly refers to cut copolyester fibers, (e.g.,staple fibers), and uncut copolyester filaments, (e.g., POY).

Dyeing copolyester fibers and spandex fibers at reduced temperaturesprevents the degradation of the stretch properties possessed by spandex.In conventional polyester-spandex blended textiles, dyeing temperaturesof about 265° F. are required to adequately dye the conventionalpolyester fibers. Unfortunately, such high temperatures weaken suchhigh-power stretch polyurethane filaments. Consequently, dyeing blendsof copolyester and spandex at lower temperatures is advantageous.

In other embodiments of the method, copolyester fibers, whether staplefibers or POY, are blended with cotton fibers. The preferredcopolyester/cotton blends include between about 5 percent and 95 weightpercent cotton fibers with the remainder comprising the copolyesterfibers. Most preferably, the blend includes between about 30 weightpercent and 70 weight percent cotton fibers with the remaindercomprising the polyester fibers. In this regard, the invention providesthe opportunity to increase the synthetic content of blended cotton andpolyester yarns to take advantage of the desirable characteristics ofthe copolyester in the resulting yarns and fabrics. For example, unlikeconventional unmodified polyester filaments, the copolyester filamentsformed according to the present method possess static-dissipationproperties that are substantially similar to cotton. Moreover, thepresent copolyester filaments retain the desirable dimensional stabilitycharacteristics of conventional polyesters.

Those familiar with textile terminology will understand that “spinning”refers to two different processes. In one sense, the term “spinning”refers to the production of synthetic polymer filaments from a polymermelt. In its older, conventional use, the term “spinning” refers to theprocess of twisting a plurality of individual fibers into yarns. The useof both of these terms is widespread and well understood in this artsuch that the particular use herein should be easily recognized by thoseof ordinary skill in the art.

Conventional techniques of polymerizing polyester and spinning filamentsare well known by those having ordinary skill in the art. Accordingly,the following example highlights the inventor's modifications toconventional process steps to achieve an especially desirable fabric.

EXAMPLE

Melt Polymerization—The copolyester composition was polymerized likestandard polyethylene terephthalate, except that the polymerizationtemperature was 10° C. lower than normal. Polyethylene glycol, having anaverage molecular weight of 400 g/mole, was injected into the processbefore the initiation of the polymerization at a rate sufficient toyield 10 weight percent polyethylene glycol in the copolyestercomposition. Likewise, pentaerthyritol was added before polymerizationat a rate that would yield 500 ppm in the copolyester composition. Thecopolyester was then extruded, quenched, and cut. The quench water was10° C. colder than normal. The copolyester was crystallized 10° C. lowerthan normal. The copolyester was melt polymerized to an intrinsicviscosity of 0.62 dl/g.

Solid State Polymerization—The copolyester chip was solid statepolymerized like a normal polyethylene terephthalate bottle resin chipexcept that the chip was maintained at 190° C. for five hours. Theintrinsic viscosity of the copolyester chip was increased in the solidphase to about 0.77 d/g.

Filament Spinning—The copolyester formed POY like a conventionalpolyethylene terephthalate product having the same filament count,except that the spinning speed was reduced by seven percent and thespinning temperature was reduced by 15° C.

Texturing—The POY was textured on a contact heater false twist texturingmachine with polyurethane disks. The POY processed like standardpolyethylene terephthalate POY except that the 100-filament product useda 2-5-1 stainless-polyurethane-stainless disk stack. Moreover, thetemperature was about 50° C. to 60° C. below normal primary-heatertemperatures. Finally, the secondary heater was not used, yielding astretch textured yarn.

Fabric Formation—Fabric formation was identical to conventionaltechniques.

Dyeing—Dyeing was the same as conventional techniques except that nocarrier was used and the batch was held at a dye temperature of 220° F.for 30 minutes.

Finishing—Finishing was the same as conventional techniques except thatthe zone temperature was reduced 10° C. and no finish was used in thepad.

In the drawings and the specification, typical embodiments of theinvention have been disclosed. Specific terms have been used only in ageneric and descriptive sense, and not for purposes of limitation. Thescope of the invention is set forth in the following claims.

That which is claimed is:
 1. A method of preparing polyethylene glycolmodified copolyester filaments, comprising: copolymerizing polyethyleneglycol and a chain branching agent into polyethylene terephthalate inthe melt phase to form a copolyester composition; wherein thepolyethylene terephthalate is present in the copolyester composition inan amount sufficient for a filament made from the copolyestercomposition to possess dimensional stability properties substantiallysimilar to those of conventional polyethylene terephthalate filaments;wherein the polyethylene glycol has an average molecular weight lessthan about 5000 g/mol and is present in an amount sufficient for afilament made from the copolyester composition to possess wicking,drying, and static-dissipation properties that are superior to those ofconventional polyethylene terephthalate filaments; and wherein the chainbranching agent is present in the copolyester composition in an amountof less than about 0.0014 mole-equivalent branches per mole ofstandardized polymer, the standardized polymer being unmodifiedpolyethylene terephthalate; thereafter polymerizing the copolyestercomposition in the solid phase until the copolyester composition iscapable of achieving a melt viscosity that facilitates the spinning offilaments; and thereafter spinning filaments from the copolyestercomposition.
 2. A method of preparing copolyester filaments according toclaim 1, wherein the weight fraction of polyethylene glycol in thecopolyester composition is between about 4 percent and 20 percent.
 3. Amethod of preparing copolyester filaments according to claim 1, whereinthe weight fraction of polyethylene glycol in the copolyestercomposition is between about 8 percent and 14 percent.
 4. A method ofpreparing copolyester filaments according to claim 1, wherein the weightfraction of polyethylene glycol in the copolyester composition isbetween about 10 percent and 12 percent.
 5. A method of preparingcopolyester filaments according to claim 1, wherein: the chain branchingagent is pentaerythritol; and the pentaerythritol is present in thecopolyester composition in an amount of less than 500 ppm.
 6. A methodof preparing copolyester filaments according to claim 1, wherein: theweight fraction of polyethylene glycol in the copolyester composition isbetween about 10 percent and 12 percent; and the step of polymerizingthe copolyester composition in the solid phase comprises solid statepolymerizing the copolyester composition until the copolyester iscapable of achieving a melt viscosity of between about 2500 and 3000poise when heated to 260° C.
 7. A method of preparing copolyesterfilaments according to claim 1, wherein the weight fraction ofpolyethylene glycol in the copolyester composition and the intrinsicviscosity of the copolyester after solid state polymerization aredefined by the shaded region of FIG.
 1. 8. A method of preparingcopolyester filaments according to claim 1, wherein: the step ofcopolymerizing polyethylene glycol and chain branching agent intopolyethylene terephthalate in the melt phase comprises copolymerizingpolyethylene glycol and chain branching agent into polyethyleneterephthalate in the melt phase to an intrinsic viscosity of less thanabout 0.65 dl/g; and the step of polymerizing the copolyestercomposition in the solid phase comprises further polymerizing thecopolyester composition in the solid phase to an intrinsic viscositygreater than the intrinsic viscosity achieved via the meltpolymerization.
 9. A method of preparing copolyester filaments accordingto claim 8, wherein the step of copolymerizing polyethylene glycol andchain branching agent into polyethylene terephthalate in the melt phasecomprises copolymerizing polyethylene glycol and chain branching agentinto polyethylene terephthalate in the melt phase to an intrinsicviscosity of less than about 0.60 dl/g.
 10. A method of preparingcopolyester filaments according to claim 8, wherein the weight fractionof polyethylene glycol in the copolyester composition and the intrinsicviscosity of the copolyester after solid state polymerization is definedby the shaded region of FIG.
 1. 11. A method of preparing copolyesterfilaments according to claim 1, further comprising the step of formingthe copolyester composition into chips after the step of copolymerizingpolyethylene glycol and a chain branching agent into polyethyleneterephthalate in the melt phase and before the step of polymerizing thecopolyester composition in the solid phase.
 12. A method of preparingpolyethylene glycol modified copolyester filaments, comprising:copolymerizing polyethylene glycol and chain branching agent intopolyethylene terephthalate in the melt phase to form a copolyestercomposition having an intrinsic viscosity of less than about 0.65 dl/g;wherein the polyethylene terephthalate is present in an amountsufficient for a filament made from the copolyester composition topossess dimensional stability properties substantially similar to thoseof conventional polyethylene terephthalate filaments; wherein thepolyethylene glycol has an average molecular weight less than about 5000g/mol and is present in an amount sufficient for a filament made fromthe copolyester composition to possess wicking, drying, and staticdissipation properties that are superior to those of conventionalpolyethylene terephthalate filaments; and wherein the chain branchingagent is present in the copolyester composition in an amount of lessthan about 0.0014 mole-equivalent branches per mole of standardizedpolymer; thereafter polymerizing the copolyester composition in thesolid phase until the copolyester is capable of achieving a meltviscosity of at least about 2000 poise when heated to 260° C.; andthereafter spinning filaments from the copolyester composition.
 13. Amethod for producing copolyester filaments according to claim 12,further comprising dyeing the copolyester filaments at a temperature ofless than about 240° F.
 14. A method for producing copolyester filamentsaccording to claim 13, wherein the step of dyeing the copolyesterfilaments at a temperature of less than about 240° F. comprises dyeingthe copolyester filaments at or below a temperature defined by theboiling point of water at atmospheric pressure.
 15. A method ofpreparing copolyester filaments according to claim 12, wherein theweight fraction of polyethylene glycol in the copolyester composition isbetween about 4 percent and 20 percent.
 16. A method of preparingcopolyester filaments according to claim 12, wherein the weight fractionof polyethylene glycol in the copolyester composition is between about 8percent and 14 percent.
 17. A method of preparing copolyester filamentsaccording to claim 12, wherein the weight fraction of polyethyleneglycol in the copolyester composition is between about 10 percent and 12percent.
 18. A method of preparing copolyester filaments according toclaim 12, wherein the weight fraction of polyethylene glycol in thecopolyester composition and the intrinsic viscosity of the copolyesterafter solid state polymerization is defined by the shaded region of FIG.1.
 19. A method of preparing copolyester filaments according to claim12, wherein: the chain branching agent consists essentially ofpentaerythritol; and the pentaerythritol is present in the copolyestercomposition in an amount of less than 500 ppm.
 20. A method of preparingcopolyester filaments according to claim 12, further comprising the stepof forming the copolyester composition into chips after the step ofcopolymerizing polyethylene glycol and a chain branching agent intopolyethylene terephthalate in the melt phase and before the step ofpolymerizing the copolyester composition in the solid phase.